The present invention relates to a reclaiming process for zeolite-containing substances used for treating sewage containing ammoniacal nitrogen.
It is a well-known fact that natural zeolite, synthetic zeolite or aluminosilicate akin to zeolite (these substances are hereinafter called zeolite-containing substance collectively) are very effective in removing ammoniacal nitrogen contained in sewage. However, their adsorption capacity is not great so that, when it is intended to reuse a zeolite-containing substance once used in removing ammoniacal nitrogen by adsorption, it is necessary to conduct a reclamation treatment to separate ammoniacal nitrogen.
The present inventors have previously proposed a process for reclaiming zeolite-containing substances by heating in an invention entitled "Process for Treating Active Sludge by utilizing Zeolite" (cf. Japanese Patent Application No. 12353/1947 and Japanese Laid-Open Application No. 82661/1948), but proposed in the present invention is a process for reclaiming zeolite-containing substances by means of chemicals.
The foregoing zeolite-containing substance is crystalline aluminosilicate having the formula Me.sub.2/n O.Al.sub.2 O.sub.3.xSiO.sub.2.yH.sub.2 O wherein Me represents alkali or alkaline earth metal, n represents the valence thereof, and x and y respectively represent coefficients. In the above general formula, the cation Me is normally Na. However, as it has exchangeability, ion-exchange thereof for calcium cation, ammonium cation, etc. is possible, and because of this characteristic, zeolite-containing substances can be utilized as the hard-water softening agent or the ammonia-containing sewage treating agent.
The ammonium cation retained by zeolite-containing substances as a result of ion-exchange can be re-exchanged for another cation, and through this re-exchange, the ammonium cation adsorbability of zeolite-containing substances can be restored. In this case, however, it is required to select an appropriate reclaiming liquid; otherwise, there will take place such troubles as the generation of scales within the reclaiming apparatus and/or the degeneration of ammonium cation adsorbability of zeolite-containing substances after reclamation. Heretofore, as the reclaiming liquid, an aqueous solution of CaO, an aqueous solution of Ca(OH).sub.2 or solutions prepared by adding NaCl to these aqueous solutions have been popular. However, these conventional reclaiming liquids are undesirable in view of the fact that there is a fear of generation of scales at the time of reclamation of zeolite and besides there is a fear of generation of scales also at the time of stripping ammonia concentrated in the reclaiming liquid in order to reclaim the reclaiming liquid per se.